“The top collapsed on people, so there were many injuries,” he said, referring to the overhead luggage compartments, before an airport official whisked him back into the Reflection Room, a quiet center in the airport for thought and meditation.

It was not immediately clear what caused this plane to lose control on a clear summer morning. The National Transportation Safety Board said it had dispatched a team from Washington to investigate, and declined to speculate. But witnesses said the plane approached the airport at an awkward angle, and it appeared that its tail hit before it bounced down the runway. When it stopped, they said, passengers had scant time to escape before a blaze burned through the fuselage.

“I looked up out the window and saw the plane coming in extremely fast and incredibly heavy,” said Isabella Lacaze, 18, from Texas, who saw the crash from the San Francisco Airport Marriott Waterfront.

“I remember watching the nose go to the ground and the tail way up in the air and then the tail back to ground hard,” Lacaze said. At that point, she said, the tail snapped off and the rest of the plane skidded down the runway.

“The smoke was not bad at all at first,” she said. “It was like one cloud. It took maybe a minute or two for the chutes to come out of the side,” she said, and people began to pour out almost immediately.

“The back got the worst of it,” a passenger on the plane, Elliot Stone, told CNN. He said the plane seemed to be coming in at a sharp angle and just as they reached the runway, it seemed to gain speed. It struck the tarmac with tremendous force, he said, and the people in the back of the plane “got hammered.” “Everybody’s head goes up to the ceiling,” he said.

Some passengers scrambled out of the plane even before the chutes deployed, he said. A number of people lay injured near the wreckage for 20 to 30 minutes before ambulances arrived, Stone said. Many people got off relatively unscathed, he said, but he saw at least five people with severe injuries.

David Eun, who said in a Twitter message that he had been a passenger on the plane, posted a photograph of a downed Asiana jetliner from ground level, which showed some passengers walking away from the aircraft.